This paper reports the electrical conductivity and Seebeck coefficient (thermopower) values derived for TiO2 (rutile) at a temperature range of 923-1353 K and p(O2) of 5 Pa-100 kPa. The effect of high-temperature treatment on the electrical properties of polycrystalline samples is discussed in terms of defect models. Samples sintered at greater than or equal to1573 K, as well as the single crystals, show n- to p-type transition, whereas samples sintered at 1473 K remain n-type throughout testing. No effect of grain size on thermopower is observed. These results are consistent with the defect disorder model assuming that titanium vacancies formed during high-temperature treatment (1473-1673 K) are frozen at the measuring temperature (923-1323 K).